The present invention relates generally to stabilizers used in self-steering axle suspension systems for wheeled vehicles. More particularly, the present invention relates to a rotary damper used as a stabilizer in self-steering axle suspension systems for wheeled vehicles to suppress oscillations during travel of the vehicle and to control the steerability of the self-steering axle suspension system.
Self-steering axle suspension systems in the medium and heavy duty truck and semi-trailer industry are known.
Typically, such suspensions are made self-steering by adjusting the pitch or caster angle of the wheels so that the drag of the wheels as the vehicle proceeds in the forward direction causes the suspension (including the wheels of the system) to steer automatically in response to steering of the (typically front) steering axle of the vehicle and in response to steering created by other vehicle motion such as vehicle cornering (i.e., as the vehicle goes into a turn). Typical of self-steering axle suspension systems are those referred to as pusher, tag or trailing axles found on trucks and semi-trailers. They may be of the liftable or non-liftable type.
In most self-steering axle suspensions in common use, a pair of dampers is used to suppress (dampen) oscillations during automatic steering at the self-steering axle resulting from travel of the vehicle. Typically, such dampers are in the form of conventional shock absorbers either with, or without, an external auxiliary coil spring. Such devices are often referred to as stabilizers for the self-steering axle suspension systems and they control the steerability of the suspension. In such a damper, a cylinder is provided which houses a fluid reservoir that is almost completely filled with an incompressible hydraulic fluid. This cylinder is separated into two chambers by a piston having an orifice, or orifices, in its head, thus to form a flow path between the two chambers, but which otherwise seals the two chambers against fluid flow therebetween. Dampening is accomplished by attaching one end of the stabilizer (usually by a piston rod connected to the piston head) to one of the components of the steering assembly of the suspension and the other end of the stabilizer to the axle beam structure of the suspension or vehicle. Since the orifice(s) in the piston head restricts flow between the two chambers as the piston slides in the cylinder due to oscillations experienced during vehicle operation (e.g. road shocks and wheel shimmy), such oscillations are appropriately dampened and tracking is stabilized.
FIG. 1 illustrates a conventional self-steering axle suspension system generally designated by reference numeral 10. Conventional self-steering axle suspension system 10 includes linear stabilizers generally designated 12, 14. Stabilizers 12, 14 are in the form of a pair of laterally extending shock absorbers 16, 18 having auxiliary coil springs 20, 22. Stabilizers 12, 14 are each mounted, at one end, to a bracket, which in turn, is mounted to a laterally extending axle beam and, at another end, to a steering assembly component such as the steering arm of the steering knuckle (as shown). Stabilizers 12, 14 suppress steering oscillations during road travel of the vehicle and control the steerability of the self-steering axle suspension system 10. The coil springs 20, 22 provide a self-centering feature in known manner. Stabilizers 12, 14 are positioned in opposite orientations such that they are mirrored about the vehicle centerline in order to control the steering action and self-centering in both directions for the vehicle.
Linear stabilizers, such as those illustrated in FIG. 1 as reference numerals 12, 14 are relatively heavy, expensive, bulky and require high maintenance. With regard to the latter drawback, linear stabilizers are subject to damage due to road debris and the like. For this reason, enclosed housing designs have been implemented; however, such designs have only reduced but have not eliminated the maintenance required for linear stabilizers. In addition, maintenance operations, especially out in the field, are cumbersome and correspondingly difficult and time consuming.
In view of the foregoing, there is a need for a relatively lightweight self-steering axle suspension system stabilizer. There is also a need for a relatively inexpensive self-steering axle suspension system stabilizer. Further, there is a need for a relatively compact self-steering axle suspension system stabilizer. Moreover, there is a need for a self-steering axle suspension system stabilizer that requires little maintenance and is relatively easy to maintain.